A conventional belief about the first settlement of the Americas holds that people with ancestry from Siberia in northeastern Asia traveled into North America across the Bering Strait when it was exposed as a land bridge during the last ice age roughly 13,500 years ago.

These first settlers were thought to be the likely creators of the prehistoric Clovis culture. Remnants of this culture primarily consist of stone tools that were first excavated near Clovis, New Mexico, in 1932. Little is known about the Paleo-Indians who made the tools, but the remains of an infant boy named Anzick-1 have been associated with the Clovis. DNA analysis of Anzick-1 in 2014 revealed a genetic connection to modern Native American populations.

Although the “Clovis-first” theory concerning the earliest peopling of the Americas remained the accepted view throughout much of the 20th century, confidence in it started to crumble in the late 1980s. Archaeologists then began to find evidence for extensive seafaring and maritime colonization of places like the Ryukyu Islands off eastern Asia. Evidence for American settlements earlier than 13,500 years ago has also been mounting.

Clovis culture tools from the Rummells-Maske Site of Cedar County, Iowa. |
Bill Whittaker, Wikimedia Commons

“Understanding when, how, and who colonized the Americas remains one of the most challenging and enduring questions in archaeology,” Torben Rick of the National Museum of Natural History’s Department of Anthropology told Seeker. “One of the most important questions in American archaeology is: Who were the first Americans and how and when did they arrive?”

Todd Braje of the San Diego State University Department of Anthropology agrees.

“Thirty years ago, we thought we had all the answers,” he said. “Now, there are more questions than answers.”

Nevertheless, a somewhat clearer view of early American settlement is coming to light, and one that Rick, Braje, and their colleagues address in a new paper in the journal Science.

“There is a coalescence of data — genetic, archaeological, and geologic — that support a colonization around 20,000–15,000 years ago,” Rick said. “This doesn’t preclude earlier migrations, or suggest that we should not investigate earlier migrations, but a growing body of evidence is building on intensive research that supports the 20,000–15,000 years ago timeframe, and evidence for earlier migrations is problematic and speculative.”

In the paper, he and his colleagues mention — and question — the recent discovery of the Cerutti Mastodon site in San Diego County, California. The site contains the remains of a 130,700-year-old juvenile male mastodon, which some scientists believe was butchered by hominid that was not necessarily Homo sapiens.

One such researcher is Daniel Fisher, director of the University of Michigan Museum of Paleontology. He told Seeker that, “based on decades of experience seeing sites with evidence of human activity, and also a great deal of work on modern material trying to replicate the patterns of fractures that we see, I really know of no other way that the material of the Cerutti Mastodon site could have been produced than through human activity.”

If validated, the Cerutti find would blow a mammoth-sized hole in virtually all theories concerning when and how the Americas were first settled, given its extremely early age. For now, though, Braje, Rick, and many other archaeologists are supporting the emerging “kelp highway hypothesis.”

Fish swim through a kelp forest at the Channel Islands National Park. |
National Park Service

Braje said that “a coastal migration into the Americas was the most likely initial colonization event,” and that “the first Americans likely arrived along the Pacific coast, not crossing the open Pacific, but migrating along the Pacific Rim in boats in a step-wise fashion” starting around 20,000 years ago.

The region then, and now, is rich in aquatic and terrestrial natural resources, with a productive kelp forest and associated marine ecosystems at sea level. The researchers explained that the kelp forest extended as far south as Baja California. At that point, productive mangrove and other aquatic habitats would have been available along the Central American coast. The kelp forest then started up again in northern Peru, reaching as far south as Tierra del Fuego.

It is possible that the first people migrating to the Americas along the kelp highway and perhaps other entrance points came from different locations and cultures.

“However, there were likely limited migration corridors during the 25,000–15,000-year-ago interval,” Braje noted. “The ice-free corridor route was closed, so a terrestrial migration during this interval is unlikely. But there may have been multiple migrations during and after this interval.”

It is also possible that people traveled back and forth from the Americas to their site of origin, yet finding evidence to support such movements — much less for any early human migration routes — is tremendously challenging.

Braje explained that the first migrants to the Americas “were probably a small group of colonizing people that likely left a very small archaeological footprint.” He said that their campsites and other associated artifacts may be offshore and underwater now.

Another scientific team excavating the bottom of Florida’s Aucilla River struck archaeological gold recently, discovering a 14,500-year-old butchered mastodon bones and chipped stone tools at a site named Page-Ladson.

Archaeologists are looking for caves, rock shelters, and places where shorelines have not changed dramatically over the last 20,000 years. These locations are the most likely to yield possible finds.